On the use of kinetic energy balance for the volumetric identification of drag sources of a blunt body. Application to road vehicles

Abstract

A volumetric identification of drag sources is proposed using the Reynolds equation for the integral mean momentum and mean flow kinetic energy balance. This methodology works independently of the turbulence model used in CFD and relies on a physical interpretation. The approach, developed in the context of automotive engineering, is of general use. A road vehicle is indeed a complex multi-scale geometry and all the flow regions are interacting. As far as the kinetic energy of the mean flow is concerned, the main volumetric loss is production of turbulent kinetic energy at all relevant sub-scales of the body. The quantitative link to the power of the mean drag force is derived from first principles. For practical applications, the volume integral used to compute the volumetric losses can be decomposed in user-defined regions and integrated into optimization loops. Indeed, if losses in a given flow region are minimized, consequences can be precisely and quantitatively evidenced for all other regions. Applications to a model two-dimensional test case and a real car geometry are discussed.